All rumours are just that: rumours. Unfounded, no backing up, etc. As such, all we know is that it is an announcement on Pokemon.

One can say likely new game though, and possibly new gen due to a number of factors though (in part how darn much they have promoted this announcement, for instance). Anything more than that should be taken with a grain of salt, if that. We'll find out in a half hour at any rate.

In regards to new gen or not... well, consider the anime in Japan about to end (with a seemingly 'filler' saga to start soon after), and the fact they rushed out all the 5th gen event Pokemon already rather than doing them relatively slowly to the 4th gen (and they only lasted as long as 4th gen lasted too that time). And Game Freak had access to the 3ds dev kits for some years now too, so surely something sooner or later on the 3ds is coming out by them.